Expression systems for the production of recombinant polypeptides are well-known in the state of the art and are described by, e.g., Marino, M. H., Biopharm. 2 (1989) 18-33; Goeddel, D. V., et al., Methods Enzymol. 185 (1990) 3-7; Wurm, F., and Bernard, A., Curr. Opin. Biotechnol. 10 (1999) 156-59. Polypeptides for use in pharmaceutical applications are preferably produced in mammalian cells such as CHO cells, NS0 cells, Sp2/0 cells, COS cells, HEK cells, BHK cells and the like. The essential elements of an expression plasmid are a prokaryotic plasmid propagation unit, for example for E. coli, comprising an origin of replication and a selection marker, an eukaryotic selection marker, and one or more expression cassettes for the expression of the structural gene(s) of interest each comprising a promoter, a structural gene, and a transcription terminator including a polyadenylation signal. For transient expression in mammalian cells, a mammalian origin of replication such as the SV40 Ori or OriP can be included. As promoter, a constitutive or inducible promoter can be selected. For optimized transcription, a Kozak sequence may be included in the 5′ untranslated region. For mRNA processing, in particular mRNA splicing and transcription termination, mRNA splicing signals, depending on the organization of the structural gene (exon/intron organization), may be included as well as a polyadenylation signal.
Expression of a gene is performed either as transient or as permanent expression. The polypeptide(s) of interest are in general secreted polypeptides, and therefore contain an N-terminal extension (also known as the signal sequence) which is necessary for the transport/secretion of the polypeptide through the cell into the extracellular medium.
In general, the signal sequence can be derived from any gene encoding a secreted polypeptide. If a heterologous signal sequence is used, it preferably is one that is recognized and processed (i.e. cleaved by a signal peptidase) by the host cell. For secretion in yeast, for example, the native signal sequence of a heterologous gene to be expressed may be substituted by a homologous yeast signal sequence derived from a secreted gene, such as the yeast invertase signal sequence, alpha-factor leader (including Saccharomyces, Kluyveromyces, Pichia, and Hansenula α-factor leaders, the second described in U.S. Pat. No. 5,010,182), acid phosphatase signal sequence, or the C. albicans glucoamylase signal sequence (EP 0 362 179). In mammalian cell expression, the native signal sequence of the protein of interest is satisfactory, although other mammalian signal sequences may be suitable, such as signal sequences from secreted polypeptides of the same or related species, e.g. for immunoglobulins from human or murine origin, as well as viral secretory signal sequences, for example, the herpes simplex glycoprotein D signal sequence. The DNA fragment encoding for such a presegment is ligated in frame to the DNA fragment encoding a polypeptide of interest.
In WO 98/28427 a genetically or chemically prepared fusion protein comprising the Fc immunoglobulin region, a derivative or analog fused to the N-terminal portion of the OB protein is reported. A chimeric molecule, i.e. antibody fusion or fusion protein, comprising a carboxy terminal protein import sequence and an amino terminal cargo region is presented in WO 03/035892.
In US 2003/0049227 a method for the induction of a cytocidal immune response against a tumor in a mammal by administering an immunocytokine, which is a fusion protein comprising an amino-terminal immunoglobulin part and a carboxy-terminal cytokine part, is reported.
WO 91/16437 reports a soluble recombinant fused protein which is stable in the mammalian circulatory system comprising a polypeptide which contains a recognition site for a target molecule, such as a complement receptor site, and is joined to the N-terminal end of an immunoglobulin chain. A fusion protein made up of an antibody and a peptide having a biological activity is reported in US 2003/0103984.
In US 2004/0033511 an antibody-cytokine fusion protein and in US 2004/0180035 an antibody-cytokine immunoconjugate are reported. An immunotoxin comprising Gelonin and an antibody is reported in WO 94/26910.